package handler

import (
	"context"
	"encoding/json"
	"errors"
	"net/http"
	"strings"

	"github.com/prabhupadasays/spsays-bff/internal/middleware"
	"github.com/prabhupadasays/spsays-bff/pkg/realtime"
	"github.com/prabhupadasays/spsays-bff/pkg/response"
	"go.uber.org/zap"
)

// ChannelRule authorizes one family of channels.
//
// Suffix is whatever follows Prefix in the channel name (a user ID today, a
// conversation ID once chat lands). Authorize reports whether userID — the
// authenticated caller — may subscribe. Returning an error means "couldn't
// decide" (a lookup failed) and surfaces as a 500; returning (false, nil)
// means "decided: no" and surfaces as a 403.
type ChannelRule struct {
	Prefix    string
	Authorize func(ctx context.Context, userID, suffix string) (bool, error)
}

// BroadcastingAuthHandler implements the Pusher channel-authorization
// endpoint that pusher-js calls (as `authEndpoint`) before subscribing to a
// private- or presence- channel.
//
// This is the gate that makes private channels private: Soketi will not honour
// a subscription without a signature, and the signature is only minted here,
// after RequireAuth has established who the caller is and a rule has agreed
// they may listen. Unknown channels are denied by default, so adding a channel
// family is an explicit act.
type BroadcastingAuthHandler struct {
	rt     *realtime.SoketiClient
	rules  []ChannelRule
	logger *zap.Logger
}

func NewBroadcastingAuthHandler(rt *realtime.SoketiClient, logger *zap.Logger, rules ...ChannelRule) *BroadcastingAuthHandler {
	return &BroadcastingAuthHandler{rt: rt, rules: rules, logger: logger}
}

// NotificationsRule allows a user to subscribe to their own notification
// channel and nobody else's.
func NotificationsRule() ChannelRule {
	return ChannelRule{
		Prefix: "private-notifications.",
		Authorize: func(_ context.Context, userID, suffix string) (bool, error) {
			return suffix != "" && suffix == userID, nil
		},
	}
}

type broadcastingAuthResp struct {
	Auth        string `json:"auth"`
	ChannelData string `json:"channel_data,omitempty"`
}

// writeAuth emits the auth payload BARE, deliberately bypassing the API's
// {success, data} envelope.
//
// This endpoint speaks Pusher's protocol, not our API's: pusher-js reads
// `auth` off the top level of the parsed body, so an enveloped response makes
// every private subscription fail. Errors still use response.Error — the
// client only checks the status code on that path.
func writeAuth(w http.ResponseWriter, payload broadcastingAuthResp) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	_ = json.NewEncoder(w).Encode(payload)
}

// Handle — POST /api/v1/broadcasting/auth. Session-authenticated (the cookie
// travels because the frontend sets credentials: "include").
//
// pusher-js posts application/x-www-form-urlencoded by default; JSON is
// accepted too so a custom client isn't forced into form encoding.
func (h *BroadcastingAuthHandler) Handle(w http.ResponseWriter, r *http.Request) {
	userID := middleware.UserID(r.Context())
	if userID == "" {
		// RequireAuth should have caught this; refuse rather than sign.
		response.Error(w, http.StatusUnauthorized, "authentication required")
		return
	}

	socketID, channel := parseBroadcastingAuthReq(r)
	if socketID == "" || channel == "" {
		response.Error(w, http.StatusBadRequest, "socket_id and channel_name are required")
		return
	}

	rule, suffix, found := h.match(channel)
	if !found {
		// Default-deny. An unrecognised channel is a client bug or an
		// probe — either way there's nothing to sign.
		h.logger.Warn("broadcasting auth: unknown channel",
			zap.String("channel", channel), zap.String("user_id", userID))
		response.Error(w, http.StatusForbidden, "channel not available")
		return
	}

	allowed, err := rule.Authorize(r.Context(), userID, suffix)
	if err != nil {
		h.logger.Error("broadcasting auth: authorize failed",
			zap.String("channel", channel), zap.Error(err))
		response.Error(w, http.StatusInternalServerError, "could not authorize channel")
		return
	}
	if !allowed {
		h.logger.Warn("broadcasting auth: denied",
			zap.String("channel", channel), zap.String("user_id", userID))
		response.Error(w, http.StatusForbidden, "not permitted on this channel")
		return
	}

	if strings.HasPrefix(channel, "presence-") {
		auth, channelData, err := h.rt.AuthorizePresence(socketID, channel, realtime.PresenceData{UserID: userID})
		if err != nil {
			h.authError(w, err)
			return
		}
		writeAuth(w, broadcastingAuthResp{Auth: auth, ChannelData: channelData})
		return
	}

	auth, err := h.rt.AuthorizeChannel(socketID, channel)
	if err != nil {
		h.authError(w, err)
		return
	}
	writeAuth(w, broadcastingAuthResp{Auth: auth})
}

// match finds the rule owning this channel and returns the part of the name
// after its prefix.
func (h *BroadcastingAuthHandler) match(channel string) (ChannelRule, string, bool) {
	for _, rule := range h.rules {
		if strings.HasPrefix(channel, rule.Prefix) {
			return rule, strings.TrimPrefix(channel, rule.Prefix), true
		}
	}
	return ChannelRule{}, "", false
}

func (h *BroadcastingAuthHandler) authError(w http.ResponseWriter, err error) {
	if errors.Is(err, realtime.ErrNotConfigured) {
		response.Error(w, http.StatusServiceUnavailable, "realtime is not configured")
		return
	}
	h.logger.Error("broadcasting auth: signing failed", zap.Error(err))
	response.Error(w, http.StatusBadRequest, err.Error())
}

// parseBroadcastingAuthReq reads socket_id / channel_name from either a form
// body (pusher-js default) or a JSON body.
func parseBroadcastingAuthReq(r *http.Request) (socketID, channel string) {
	if strings.HasPrefix(r.Header.Get("Content-Type"), "application/json") {
		var body struct {
			SocketID    string `json:"socket_id"`
			ChannelName string `json:"channel_name"`
		}
		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
			return "", ""
		}
		return strings.TrimSpace(body.SocketID), strings.TrimSpace(body.ChannelName)
	}
	if err := r.ParseForm(); err != nil {
		return "", ""
	}
	return strings.TrimSpace(r.PostFormValue("socket_id")), strings.TrimSpace(r.PostFormValue("channel_name"))
}